This invention relates to an image data storing device in which binary image data are stored in a memory means having a large capacity.
FIG. 1 outlines a conventional image processing device. In FIG. 1, reference numeral 1 designates an image input device; 2, a large capacity memory unit; 3, an image output device; 4, a CPU, and 5, the main memory of the CPU 4. In this image processing device, an image is read as binary signals by the image input device 1, and is stored in the large capacity memory unit 2 through the main memory 5. Thereafter, in response to an instruction from the CPU, the binary signals are suitably processed, so that the image is outputted by the image output device 3.
In order to read an image with high quality with the image input device, each picture element shoud be about 1/12 mm in size. For instance, if the entire area of a sheet of "B4" size (364 mm.times.257 mm) is read with 1/12 mm.sup.2 per picture element, then the amount of data on one sheet is about 1.7 M bytes.
In general, a magnetic disc is employed as the large capacity memory unit Z. In the case where an 8-inch commercially available disc is employed as the large capacity memory unit 2, the memory capacity is about 40 M bytes at maximum. Therefore, if the conventional image processing device is used to store an image of the aforementioned "B4" sized sheets, the magnetic disc can store data for no more than twenty-three such sheets.
Recently, a laser scan type image printer has been developed for use as the image output device 3. That is, the image output device may operate at a high speed, and some such image output devices have an average video rate of about 20 M bits/sec. On the other hand, the data transfer rate between the large capacity memory unit 2 and the main memory 5 is of the order of 7 M to 8 M bits/sec. Therefore, the data transfer rate between the large capacity memory unit 2 and the main memory 5 becomes an obstruction or bottleneck in the operation of outputting the image stored in the large capacity memory unit 2 from the image output device 3. Thus, the conventional image processing device is insufficient in systematic capability. This is another drawback of the conventional device.